Sabenapilot From Belgium, joined Feb 2000, 2712 posts, RR: 48 Reply 1, posted (12 years 4 months 3 days 16 hours ago) and read 1675 times:
Hi there, Hawk21M-
Are you doing your B737 type rating or what?
Anyway, I have only flown the B737-200, so I can't aswer all of your questions on the NG, however, I can help you with this one, I think.
In aviation the aim is to keep things simple if you can, so unlike for the #1 and #2 windows, there is indeed no heating element in #3 windows, because even if it would have ice on it, you don't need to look through this side window to fly the plane anyway.
Ok, but I have never seen ice on the #3 window, although it is unheated! How can that be?
Well: in order to prevent ice from building, they have made this window from a different material, which is less likely to encounter icing then the glass windows, thanks to its improved ability to transfer heat from the cockpit. Sadly, this material has not the same strength as glass windows, for instance in case of bird strikes, which prevents it from being used in the other windows. However, ad a birdstrike will always be a frontal strike, never a sideways strike, this is no problem for the #3 window.
I don't think you'll find this explanation anywhere in the manual; it's just something I have come up with myself, but I think it is quite a good one...
Sabenapilot From Belgium, joined Feb 2000, 2712 posts, RR: 48 Reply 3, posted (12 years 4 months 3 days 14 hours ago) and read 1654 times:
I have looked it up in my B737-200 manual and #2 screan is actually heated too! (although not electrical, unless as an option)
The reason for this difference is in the materials that make up this screen. As #3 screen is not made out of glass (strengthened with vinyl) as #1 and #2 screens, but rather out of plexiglass with a phenolic spacer in between, there is a posiblility to heat this kind of screens without inserting a conductive coating.
(In other words it's a simplification)
#3 screen is heated by airconditioned air passing between the 2 layers of plexiglass. The reason for not using this simplified system on screens #1 and #2 as well is the fact that there's a need for a phenolic spacer to bleed the air through, resulting in a reduced strength of the screen.
HAWK21M From India, joined Jan 2001, 31450 posts, RR: 57 Reply 4, posted (12 years 4 months 3 days 12 hours ago) and read 1642 times:
Well Sabenapilot,I'am not a Pilot but An Aircraft Maintenance Engineer [AME] or Maintenance guy.
I work on the B737s classic & training for the NGs.
Since you've flown 737s I could learn something from you.
Comming to the Topic
I've seen the #3 get fogged up though,When they Taxi in, the #3 window is fogged from the outside,So I'm sure there is no heat provision.
Its very similiar to a Heat control unit malfunction on the heated windows.
Cdfmxtech....Are you sure #3 has a heater option. Are there any 737s with a heated #3.
Sabenapilot From Belgium, joined Feb 2000, 2712 posts, RR: 48 Reply 5, posted (12 years 4 months 3 days 10 hours ago) and read 1637 times:
Yes, that's right-
The #3 screen sometimes fogges up after landing, because several operators (including Sabena) cut one pack after landing to safe some money.
This means that a single pack is kept running (mainly for pax comfort) and thus the supply of fresh airconditioned air is reduced, causing the side screens to fogg up on damp days.
Sabenapilot From Belgium, joined Feb 2000, 2712 posts, RR: 48 Reply 6, posted (12 years 4 months 3 days 9 hours ago) and read 1633 times:
Since you've flown 737s I could learn something from you.
Thanks for the compliment, but I doubt it.
Most of the times mechanics know more about the plane then pilots, certainly when it comes to this kind of smaller 'details'. The only time we can really contribute to a technical discussion is when operational aspects must be taken into consideration.
Anyway, if I can be of any help, feel free to ask.
Cdfmxtech From United States of America, joined Jul 2000, 1338 posts, RR: 28 Reply 7, posted (12 years 4 months 3 days 7 hours ago) and read 1624 times:
Yes...at least the Next gens do. Straight from the standard Boeing B737 Next Gen Maintenance manual:
CONTROL CABIN WINDOW ANTI-ICING SYSTEM - WINDOW THERMAL SWITCH
Thermal switches on the No. 5 windows control power to the No. 4 and 5 windows.
Thermal switches on the No. 3 windows control power to the No. 3 windows.
Thermal switches are on the No. 5 windows.
Thermal switches are also on the No. 3 windows.
A bracket with a torsional spring secures the switch to the window.
A conductive paste improves heat transfer from the window to the switch and prevents a temperature lag between the switch and the window.
The thermal switch is a normally closed, single pole, snap action bimetallic device. It operates by thermal expansion.
The thermal switches are wired in series with the windows they control.
Put the related SIDE WINDOW HEAT switch to ON to energize the system. 115v ac power moves through a thermal switch to the resistive layer of each window. The resistance of the paste to the current produces heat and warms the window.
As the No. 5 window get warm, so does the thermal switch. The switch opens at a temperature of 110F (43C) or more. This opens the circuit, and removes power to the windows.
As the No. 3 window get warm, so does the thermal switch. The switch opens at a temperature of 95F (35C) or more. This opens the circuit, and removes power to the windows.
When the No. 5 window and thermal switch temperature decreases to 90F (32C) (nominal), the switch closes and completes the heat circuit. This starts the window heat again.
When the No. 3 window and thermal switch temperature decreases to 75F (24C) (nominal), the switch closes and completes the heat circuit. This starts the window heat again.
Training Information Point
These windows are not part of the anti-ice panel indication or test systems.
These windows do not have overheat protection. If the thermal switch fails or detaches from its conductive paste, the windows can overheat. The windows should be warm to the touch, but not hot. If bubbles appear in the window layers, this may be an indication of window overheat (thermal breakdown and outgassing of vinyl layers).
737LAME From Norway, joined Apr 2001, 75 posts, RR: 4 Reply 8, posted (12 years 3 months 4 weeks 1 day 13 hours ago) and read 1590 times:
Excellent description Cdfmxtech
The heat film on the flight deck # 3 window on a 737 is on the inside part of the window. The heat is there to keep the window de-fogged and also for pilot comfort.
A #3 window has no impact protection capability, therefore the heat on this is optional.
The airline I work for (BU) has this option and it works well.
The heating of the #1,#2,#4 & #5 is there for removing ice and also for added Impact protection.
If you have inoperative heating on one of these you will get some penalties:
1.No flight in known or forecast icing condition.
2.Limit airspeed to 250kts under 10000ft
3.Windshields de-fog system must work normal.